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I have a model in HEC-Ras version 5.0.3 that I set-up in Civil 3D 2017 (stream alignment, cross sections, LOB, ROB) and I was asked to add in the Manning roughness values from SRH2D. I was asked to do this because I was told that the .geo file from WMS brings in all of the n-values along the cross section, creating a more real-world HEC-Ras model. Currently, I have only 3 n-values.

I found a forum that displayed how to correctly transfer the materials file from SRH2D to WMS, and then create essentially the geometry file in WMS to export to HEC-Ras, but I already did most of this in Civil 3D. I don't want to re-do my .geo file in HEC-Ras because it is basically complete. Is there a way to import only the n-values from SRH2D without re-doing my entire HEC-Ras model created from Civil 3D?

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If you can get your materials file from SRH2D into a WMS "Area Property" coverage, WMS will get the Manning's roughness values from this coverage when you extract the geometry for your cross sections. To extract the geometry for your cross sections, you need a 1D Hydraulic Centerline and a 1D Hydraulic Cross Section coverage in WMS. In the centerline coverage, you would define your stream centerlines and your bank lines (bank lines are optional, but recommended). In the cross section coverage, you define your cross section locations. I think you're saying you've already created these coverages or layers in Civil 3D and you don't want to create them again. If you have your HEC-RAS geometry file, you can export a GIS Export file from HEC-RAS and read this file into WMS. The 1D Centerline and Cross Section coverages will be created if you do this, but you will need to re-extract the cross sections (including the geometry) to assign Manning's roughness values in your Area property coverage to your cross sections. Here are the steps for doing this:

6. Bring in your Manning's roughness areas as an area property coverage. Make sure you have polygons in this covearge, make sure you have defined Materials (Edit | Materials), and make sure you have a material assigned to each polygon in the coverage.

8. Generate your point properties from the arcs in the Centerline coverage and Generate your line properties from your Area Property coverage and select OK.

9. Now go to the Hydraulic Modeling Module, HEC-RAS menu and define your Manning's roughness values under the Material properties for each material type. You also want to set your model control to use the Materials (under the HEC-RAS menu, there's a Model Control menu item for doing this).